Majohnson,I think what they are referring to as "Top Dressing" in this context is the soil replacing the soil that you took off to get the tree prepared for a show. Take a look at this wonderful post on dressing a tree: http://bonsaitonight.com/2010/02/16/moss-technique/ . After you get the show moss off, you replace the normal amount of soil you took off in the first place.

What my father and I do is put yamagoki moss, http://www.satsukibonsai-en.com/misc.htm , on top of all our shohin, except conifers, and on all size satsukis. Maples like it to, but only really in the summer. The yamagoki helps to keep the trees moist, lessening a watering of 3 times on a hot STL summer day to one time, with a light misting later.

A block of yamagoki like the one I linked can be applied to quite a few trees. Once you put the stuff in water, it multiplies

I may be way off the ball, so maybe chris will come in and clarify what he meant when he made that post,

I think that there is a little over interpretation going on. When we prepare trees for show with Boon, if the tree will not be repotted just prior to the show, you do soji in the late fall/early winter, remove the crusty top layer of soil and replace the fertilizer/soil mixture with new bonsai soil (this is actually done for all trees, with extra attention paid to trees not being repotted that year). When getting the tree ready to show, a portion of the top layer will be removed to lower it enough for the moss (garden mosses) to be applied (artfully) and not have the edges of the moss showing above the edge of the pot. After the moss is applied, a fine (sifted) lava is applied to fill in the spaces between the discrete little pieces of moss to give a finished look (think of grout between ceramic tiles....).

After the show, the garden moss is usually removed and top dressing (the bonsai potting mix) is added to take the soil level up near the top edge of the pot, near not up to the top- leave a 1/4-1/8" or so edge to alow water to pool slightly before flowing down through the soil as the roots grow and fill the pot. On deciduous trees that have been recently repotted, the soil is replaced as described above, and a very thin layer of sifted NZ White Sphagnum Moss is applied to act as a slight moisture holding layer and for its benefits on new root development. If you have Yamagoki, it does the same.

The confusion arising from Chris's article is that he also talks about replacing the missing soil on conifers (due to the removal of soil for moss placement and its subsequent removal after the show) with the fine sifted lava particles. Aesthetically, this can be quite pleasing, it allows trees in the yard to look quite pleasing, even after you start applying fertilizer. You can gain the exact same efect on tree growth and health by replacing the top layer of soil with top dressing bonsai mix, like the deciduous trees. Typically we use a soil that is slight smaller than the main mix for top dressing, again aesthetics and possibly to slightly reduce evaporation, particularly on large trees (large trees tend to have a slightly coarser mix than medium trees which is slightly coarser than small trees).

Perhaps key to this all, is that trees that are placed in bonsai pots should not have a rounded/elevated soil profile when viewed at pot lip/edge level. The soil should be flat and level leading to the tree. The exceptions are bunjin trees in nanban pots and tray landscapes where rock or other elevations have been introduced. The number one criticism that we get for repotted trees is that they sit too high in the pot at repotting, and either need to have more of the rootball removed to allow the tree to set in its pot appropriately, or placed in a deeper pot. Take a look at the trees that Bill Valvanis and Boon have posted, look at the Kokufu tree pictures, those trees set appropriately in their pots. All of the pre and post show prep that we have discussed here is predicated on havng the tree firmly and appropriately placed in its pot.

MAJohnson, you read Chris' posts and you get great information. The error many folks make is to not apply those techniques that make for good show trees during development. Good repotting and soil maintenance principles help to make trees better during development- and get the patterns set for later on. John